The public is generally aware that driving with under-inflated tires is undesirable. However the actual pressure within conventional automobile pneumatic tire is not easy for the driver to determine. Visually, under-inflation is not apparent until it is acute. When a puncture has occurred while driving the driver may have no indication until the under-inflation is acute.
The automotive industry has long recognized that driving with under-inflated tires is unsafe, because the automobile becomes increasingly unstable as the under-inflation increases, possibly leading to a serious accident. In addition, driving with under-inflated tires causes increased fuel consumption, with the consequent greater national consumption of, and dependance on, imported oil.
The industry has, over several decades, proposed various designs to alert a driver to any under-inflated tires of the vehicle while driving the vehicle. Illustrative are the disclosures of the following United States patents:
U.S. Pat. No. 5,040,561 discloses a pressure detector for automobile tires having the following features; a post-sealed reference chamber mounted on the base of the tire valve, a pair of seals, one for the tire and the other for the reference chamber, external contacts closing when the tire is under-inflated, a transmitter inside the tire at the foot of the pedestal, the transmitter sending a signal of under-inflation. A receiver is described generally, but is not disclosed.
U.S. Pat. No. 5,065,134 discloses a pressure detector for automobile tires having the following features; the detector mounted on the rim of the wheel, a reference chamber 20 inflated and pre-sealed at installation, a signal generator attached to the frame adjacent to the detector, the generator causing a signal within the circuit of the detector when the tire is rotated, a warning indicator 17 which gives off an alarm signal when a tire has low pressure, the threshold pressure rising as the speed increases by inertial forces on the flexible diaphragm.
U.S. Pat. No. 5,463,374 discloses a pressure detector for automobile tires having the following features; a transmitter circuit closed by an inertial switch when the vehicle reaches a speed of 25 mph, a battery with life equal to the life of the vehicle, a receiver and display tied into a keyless alarm system, a transmitter in sleep mode until queried.
U.S. Pat. No. 5,557,256 discloses a pressure detector for automobile tires having the following features; a detector mounted outside the valve stem of the tire, a post-sealed reference chamber, a permanent magnet moved by the deflectable wall of the reference chamber, a hand-held device to detect the actual pressure of the tire, necessarily when the vehicle is stopped.
The proposals of the prior art have various drawbacks, proven by the fact that these detectors have not been widely adopted despite the decades of research devoted to their adoption. Among the problems are that some detectors are quite complex, some are quite expensive, others require substantial modification of existing automotive components, and some are simply not adapted for retrofitting on existing vehicles.